The present invention relates to thermoplastic sheet having a surface contour which permits the sheet to expand and contract under extreme ambient temperatures without rupturing.
Thermoplastic polymers such as graft acrylonitrile-butadiene-styrene (ABS) are being used more and more as a substitute for other materials in structures where large flat sheets or plates are utilized, such as, for example, in refrigerator car door liners, in camper bodies and the like. In such applications the ambient temperature may range from -40.degree. C. to +80.degree. C. Under such extreme temperature differences the thermoplastic sheet expands and contracts and will rupture on expansion unless the sheet is properly designed from a structural standpoint. In smaller structures it may only be necessary to provide mounting apertures of a size to permit the sheet to move within its mounting. In larger structures, however, other means must be provided to permit the thermoplastic sheet to expand without consequent rupturing or tearing. It is therefore common practice to corrugate the sheet to permit expansion without rupture. However, this permits expansion in only one direction and is not satisfactory for such large applications as the panel for refrigerated transport containers.
The present invention provides a structure which permits the sheet or panel to the firmly attached or connected to its mounting and to absorb internal stresses and strains due to extreme temperature changes.